bpf, perf: use more lightweight barriers
bpf, perf: use more lightweight barriers

While perf tool itself uses full rmb(), mb() for walking the ring it
turns out they are not needed and haven't been updated in a long long
time, so smp_rmb() and smp_mb() can be used instead which are more
lightweight. Also fix fallback to be generic __sync_synchronize() for
everything non-x86.

Signed-off-by: Daniel Borkmann <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@iogearbox.net>

tklauser/cilium,michi-covalent/cilium,tgraf/cilium,scanf/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,cilium-team/cilium,scanf/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,scanf/cilium,cilium-team/cilium,cilium/cilium,tgraf/cilium,scanf/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium,cilium/cilium,scanf/cilium,scanf/cilium,scanf/cilium